As mechanical systems and devices become more complex through the incorporation of microprocessors and other electronics, the use of, and reliance on, sensors have become increasingly important for monitoring the operation of these types of systems and devices.
Rotary and linear sensors are frequently used to detect and report the location or position of a shaft or other mechanical linkage with reference to a known position. This known position, or zero-point, is considered the origin from which to measure and calculate displacement values. For example, a shaft may rotate 80 degrees from the zero-point or −25 degrees from the zero-point. The sensor detects this rotary displacement relative to the zero-point and provides an output signal or value indicative of the detected displacement.
For a sensor to accurately indicate or report displacement (angular or linear), the condition in which the sensor produces a zero output must coincide with the physical zero position of the mechanical linkage being sensed.
In the past, when a sensor was connected to a mechanical system, the proper alignment of the sensor and linkage was accomplished using such mechanisms as set screws, mechanical offsets, variable spacers, etc.
FIG. 1 depicts an exemplary prior art rotary sensor arrangement 100. According to this arrangement, a sensor 102 has an input voltage 112 that is modulated according to the sensor's physical condition in order to produce an output signal 114. The sensor 102 has a rotary shaft 104 whose position relative to a zero-point controls the value of the output signal 114. A device designer using the sensor 102 would have data sheets that provide a description of the sensor 102 including the range of values for the output signal 114 and the correspondence between the value and the rotary position of the shaft 104.
An annular unit 110 provides mechanical and operative coupling between the sensor shaft 104 and a shaft 106. The shaft 106, for example, can be a steering valve, a shaft connected to an acceleration pedal, or some other control linkage. Because of the coupling unit 110, as the control shaft 106 rotates, the sensor shaft 104 rotates as well.
Within the mechanical system of control shaft 106 (e.g., a forklift, an automobile, etc), there is some objective physical position corresponding to zero displacement of that control linkage or shaft 106. Similarly, there is a physical position of the sensor shaft 104 that corresponds to the sensor 102 reporting zero displacement. For the sensor and control system to operate effectively, these two zero positions should be aligned.
Set screws 108a and 108b are used when aligning the different shafts 104 and 106. This alignment arrangement has a number of drawbacks including being time and labor intensive. Another problem is that the set screws 108a and 108b bite into the shaft material to provide a grip. This results in shaft scars that cause subsequent zero adjustments to become much more difficult when the sensor needs to be realigned. Similar problems exist in linear sensors where a sensor or shaft mountings need to be adjustable, or otherwise offset, so that sensors and their control shafts can be properly aligned.
A need, therefore, exists for a sensor zero-point alignment procedure and device wherein the zero-point alignment can be performed in an efficient manner and multiple times over the lifetime of a system.